1. Field of the Invention
The present invention relates to in-line grinding or milling apparatus in general which size and disperse solids contained in a liquid slurry as they are pumped through it and more particularly to machines with adjustable rotors having a number of stator-rotor combinations interchangeably mountable in the machine to accomplish a wide variety of size reduction needs. The present invention also pertains to the use of such in-line grinding apparatus in drill cuttings disposal systems wherein the cuttings are treated and refined to form a slurry to be pumped into an earth formation through a well bore.
2. General Background
It is well known within the art that a stator-rotor assembly composed of intermeshing teeth or shear blocks may be use in the sizing of both flexible and friable solids. However, heretofore, fine grinding of such solids produced by such methods have been done by different machines, i.e. ball, or roller mills and fine shredders and the like.
An apparatus for grinding solids as they are pumped through the machine has been disclosed in U.S. Pat. Nos. 5,495,986 and 5,586,729. The apparatus disclosed the concept of utilizing an adjustable rotor in combination with intermeshing teeth or shear blocks to accomplish the size reduction of solids in a liquid slurry. An arrangement of the intermeshing teeth further discloses a tooth arrangement which allows the gap between the stator and rotor to be set for any desired particle size. However, the apparatus does not teach a structure for performing such adjustment nor does it teach a method for interchangeably adapting non-intermeshing rotor and stator elements.
It has now become evident that a need exists for fine grinding solids entrained in a slurry to micron size. Ideally such fine grinding should be accomplished with the same machine configured to receive interchangeable stator-rotor assemblies capable of shearing and or fine grinding particles to micron size. For example, the disposal of drill cuttings from drilling various types of wells has become an increasingly difficult problem due to restrictions imposed by various governmental authorities and the desire to minimize environmental damage. These problems are aggravated, or at least amplified, in certain well drilling operations, particularly in offshore drilling operations, wherein the disposal of drill cuttings normally requires transport of the cuttings to a suitable landfill or shore-based processing system.
One solution to drill cuttings disposal has been to separate the drill cuttings from the drilling fluid and reclaim coarse cuttings for use as construction grade gravel. Finer particles of material are slurried and injected into an earth formation through a disposal well. In many instances, however, disposal of all of the drill cuttings is not as conveniently handled. This is especially evident in offshore well drilling operations where the separated cuttings are not suitable for reuse, reclamation or other disposal processes. The cost of managing drill cuttings has increased dramatically as the offshore platforms migrated into deeper waters which further increases the distance to land-based disposal operations.
U.S. Pat. No. 5,129,469 illustrates a method and system for processing drill cuttings whereby drill cuttings are reduced in particle size by using a centrifugal pump as the grinding means of size reduction. After size reduction, the drill cuttings slurry is injected back into the formation through the well bore. It has been found in practice that the centrifugal pump grinding means contained in the above referenced patent has no ability to produce a consistent particle size. As a result, the system operates best when used in conjunction with a shaker screen to separate oversized solids leaving the centrifugal pump grinding means. Sized solids falling through the screen are suitable for injection, whereas rejects from the screen are recirculated repeatedly through the pump grinding means until they are sufficiently small to pass through the shale shaker screen. It is therefore evident that a more efficient method and apparatus is needed to provide a consistent particle size reduction